1. Field of the Invention:
The present invention relates to the absorption of carbon dioxide by alkaline solutions. In particular, the present invention relates to the use of the absorption of carbon dioxide by alkaline solutions for the determination of pH or hydroxide concentration in an inaccessible location.
2. Discussion of Background:
It is known that alkaline solutions will absorb carbon dioxide. Methods for measuring carbon dioxide concentrations, and apparatus for implementing those methods, are described in the relevant literature. For example, Matthews, et al., in U.S. Pat. No. 4,185,195, describe a sensor for determining the partial pressure of carbon dioxide in a liquid by determining the pH of that liquid and inferring the CO.sub.2 concentration. The liquid, preferably a transparent aqueous gel, exhibits variations in pH as a function of the partial pressure of dissolved CO.sub.2.
In U.S. Pat. No. 3,660,034, Baranyi, et al., disclosed an apparatus and process for determining the maturity of fruit by absorbing, into an alkaline solution, the amount of CO.sub.2 developed by the fruit as its carbohydrates break down, then measuring the changes in electrical conductivity of the solution.
Under certain circumstances, it is not feasible or desirable to measure the pH or the carbon dioxide concentration of a solution. For example, the solution may be located in a remote area, where direct access to the solution for sampling is difficult or time-consuming, or the solution may be toxic or radioactive. Minimizing personnel exposure to hazardous solutions may be a legal requirement as well as, of course, a legitimate management concern. Thus, there are situations where the solution is inaccessible but concentration information about it is needed.
In industrial process control, where laboratory conditions do not exist and miscellaneous conditions that might affect the process cannot always be controlled, a correlation used to calculate a variable such as concentration by inference from measured values must be sufficiently accurate and the measurements must be easily and rapidly obtained. There is a need, then, for a method for determining the pH and hydroxide concentrations of solutions, remotely and accurately, especially when the solutions are hazardous or otherwise inaccessible.